1. Field of the Invention
The present invention relates to a motor-operated, direct-pressure type mold clamping mechanism of an injection-molding machine.
2. Description of the Related Art
An injection-molding machine is furnished with a toggle type mold clamping mechanism, in which a drive source and a moving platen are connected by means of a toggle link, or a direct-pressure type mold clamping mechanism, in which the drive source and the moving platen are connected directly. The clamping mechanism serves to open or close and clamp dies that are attached individually to the moving platen and a stationary platen.
In the mold clamping operation, the dies must be clamped with a great force. Thus, a requisite for the drive source of a mold clamping mechanism is the capability of producing a great clamping force. In the process of injection molding, moreover, the time required for the manufacture of each molding, i.e., the cycle time, is expected to be shortened. Another requisite for the drive source, therefore, is to be able to drive the dies at high speed while they are being opened or closed.
The toggle link acts so as to help the dies be opened or closed at high speed, and to facilitate the production of a great clamping force. Thus, the toggle type mold clamping mechanism fulfills both of the aforesaid requirements. The direct-pressure type mold clamping mechanism, on the other hand, has the advantage over the toggle type mold clamping mechanism that it does not require mold thickness adjustment for compensating the change of the die thickness. It is difficult for the direct-pressure type mold clamping mechanism, however, to satisfy both the aforementioned requirements. In the case of a direct-pressure type mold clamping mechanism using a motor as its drive source, for example, both those requirements can be fulfilled only if the motor used has a very large capacity, and therefore, is an expensive one. In consequence, the manufacturing cost of the injection-molding machine increases.
Also, a great clamping force can be obtained with use of a general-purpose motor if its output is enhanced by means of a reduction mechanism. In this case, however, the dies are moved by means of a speed reducer, so that the speed of mold closing and opening operations is reduced. Thus, the cycle time is lengthened, thereby lowering the production efficiency of the injection-molding machine.